Many types of gaming systems exist that let players place a wager on particular randomly selected symbol arrangements. The most common examples of these types are the so-called slot machines or fruit machines. Slot machines present several wheels or strips with symbols on them in a display area. After rotating or otherwise changing the display for a certain time, the symbols currently visible in the display area present certain combinations along certain lines, known as pay lines or win lines. If a player has selected one or more of those win lines before initiating the display change, he wins the game and may receive a monetary amount or other prize.
Slot machines may embody the symbol carriers as physical reels or wheels that rotate along a physical axis, or as virtual reels generated as computer images and displayed on the display area which is embodied as a display screen. The latter kind is commonly known as a video slot machine.
Early gaming systems would provide only a single win line: a horizontal line through the symbols lining up in the center of the display area. An example of such an arrangement is shown in FIG. 1: in display area 101 three reels are shown, with a win line 102 passing through the center of the display area 101. When the three reels stop rotating, the symbol arrangement underneath the win line 102 determines which prize, if any, the player has won. Certain winning combinations are illustrated to the right of the display area 101.
FIG. 2 shows an example of a gaming system's display with five reels, with three symbols on each reel visible at the same time. In this example, a player can place a wager on up to 25 different win lines. For example, win lines in FIG. 2 may run through the center as in FIG. 1 but may also run from top left to bottom right, or weave across the symbols in various arrangements, e.g. from top left to middle bottom to top right or across top left, top second, middle middle, bottom fourth and bottom right. Multiple win lines can be provided simultaneously, allowing players to wager on any, some or all of them.
Commonly game outcomes only include combinations of symbols consisting of at most one symbol from each reel. U.S. Pat. No. 5,611,535 proposes a compound win line that is associated with more than one symbol on a single reel. Thus, a winning game outcome can require, for example, a combination that includes two or more particular symbols from a single reel.
The symbol strips may be provided as actual wheels that rotate along an axis, or as a sequence of images displayed on a screen. For example, U.S. Pat. No. 5,807,172 discloses a method for operating a slot machine which allows a player nine ways to win for a 3-reel slot machine, where the reels are provided as actual wheels. Today virtually all such gaming systems employ electronic screens because of the flexibility they provide. Symbols can be replaced, the reels can be made much longer and many variations in win lines and winning combinations can be created using software and electronic screens. U.S. Pat. No. 4,711,451 provides an optimized implementation of a stopping mechanism for real or computer-generated (“virtual”) reels.
In addition, much thought has been put into devising ways to vary win lines to encourage player enthusiasm. U.S. Pat. No. 6,261,178 discloses an additional win line known as a “mystery line”, which is a randomly selected combination of symbol positions. A prize is paid to the player in the event that a predetermined combination of symbols is displayed in the randomly selected arrangement of symbol locations. U.S. Pat. No. 6,227,971 discloses a gaming device with two games, where certain symbols in the first game can be added to win lines in the second game. U.S. Pat. No. 6,832,957 discloses a gaming device with multiple sets of identical reels, allowing the player to wager on win lines on one or more of said sets of reels, and on predetermined combinations of gaming symbols which occur over the plurality of sets of reels.
Changing win lines may change the odds of winning combinations. U.S. Pat. No. 6,413,162 proposes to remove either the vertical or horizontal win lines, preferably the vertical win lines in order to equalize the odds of winning on any particular win line. U.S. Pat. No. 5,085,436 allows for the probability of winning combinations to be altered without changing the number of physical symbols per reel, or alternatively that the number of physical symbols per reel may be decreased, with a consequential increase in symbol size, without altering the probability of winning combinations provided on the machine occurring.
With more complex win line arrangements, allowing the player to select the desired line(s) becomes an issue worthy of attention. U.S. Pat. No. 6,093,102 discloses an arrangement whereby the number of win lines provided on a slot machine, particularly a machine with a display with 3 times 5 symbols, can be increased without changing the display format. This is achieved by allowing selection of individual symbols rather than particular lines, and by creating win lines from the selection of symbols.
However attractive such arrangements may be, there still is a need to improve gaming systems of the above-disclosed type.